• 한국분말재료학회지
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• 제14권5호
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• pp.298-302
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• 2007

In recent years, a rapid increase in demands for the soft magnetic composite parts has been created and it has been tried to improve their properties by various processing methods, alloying elements and compaction parameters. Warm compaction method has been used for the reduction of residual stress, the improvement of magnetic properties and the higher densities. In this work, the effects of warm compaction and polymer binder on magnetic properties of Fe powder core were investigated. The sintering powder, Fe oxide, was ball-milled for 30n hours. And then ball-milled Fe oxide powder was reduced through hydrogen reduction process. The hydrogen reduced Fe powder and polymer binder were mixed by 3-D turbular mixer. And then the mixed powder was warm-compacted. The magnetic properties such as core loss and permeability were measured by B-H curve analyzer.

• 한국산학기술학회논문지
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• 제5권2호
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• pp.114-117
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• 2004

비소성 Pt/MoO₃와 200℃에서 소성한 Pt/MoO₃가 150℃에서 수소를 흡착하는 속도를 측정하였다. 소성된 Pt/MoO₃의 수소 흡착량이 비소성 Pt/MoO₃의 수소 흡착량보다 증가하는 것으로 관찰되었다. 상기 두가지 흡착 속도를 나타내는 Pt/MoO₃ 촉매에서 탈착량은 흡착량과 탈착 온도의 증가에 비례하는 것을 알 수 있었다. 또한 X-Ray Photoelectron Spectroscope(XPS) 결과로부터 Pt와 MoO₃간의 활성점에 존재하는 Cl의 존재가 수소 이동 속도를 결정하는 것으로 판단되었다.

• 전기화학회지
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• 제2권1호
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• pp.38-45
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• 1999

Electrochemical lithium intercalation into a PECVD (plasma enhanced chemical vapour deposited) carbon film electrode was investigated in 1 M $LiPF_6-EC$ (ethylene carbonate) and DEC (diethyl carbonate) solution during lithium intercalation and deintercalation, by using cyclic voltammetry supplemented with ac-impedance spectroscopy. The size of the graphitic crystallite in the a- and c-axis directions obtained from the carbon film electrode was much smaller than those of the graphite one, indicating less-developed crystalline structure with hydrogen bonded to carbon, from the results of AES (Auger electron spectroscopy), powder XRD (X-ray diffraction) method, and FTIR(Fourier transform infra-red) spectroscopy. It was shown from the cyclic voltammograms and ac-impedance spectra of carbon film electrode that a threshold overpotential was needed to overcome an activation barrier to entrance of lithium into the carbon film electrode, such as the poor crystalline structure of the carbon film electrode showing disordered carbon and the presence of residual hydrogen in its structure. The experimental results were discussed in terms of the effect of host carbon structure on the lithium intercalation capability.

• 한국재료학회지
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• 제28권2호
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• pp.124-128
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• 2018

N-type porous silicon (PS) layers and thermally oxidized PS layers have been characterized by various measuring techniques such as photoluminescence (PL), Raman spectroscopy, IR, HRSEM and transmittance measurements. The top surface of PS layer shows a stronger photoluminescence peak than its bottom part, and this is ascribed to the difference in number of fine silicon particles of 2~3 nm in diameter. Observed characteristics of PL spectra are explained in terms of microstructures in the n-type PS layers. Common features for both p-type and n-type PS layers are as follows: the parts which can emit visible photoluminescence are not amorphous, but crystalline, and such parts are composed of nanocrystallites of several nm's whose orientations are slightly different from Si substrate, and such fine silicon particles absorb much hydrogen atoms near the surfaces. Light emission is strongly dependent on such fine silicon particles. Photoluminescence is due to charge carrier confinement in such three dimensional structure (sponge-like structure). Characteristics of visible light emission from n-type PS can be explained in terms of modification of band structure accompanied by bandgap widening and localized levels in bandstructure. It is also shown that hydrogen and oxygen atoms existing on residual silicon parts play an important role on emission stability.

• 한국진공학회지
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• 제8권2호
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• pp.165-171
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• 1999

Diamond-like carbon(DLC) films were synthesized using the rf-plasma CVD technique with the addition of small amounts of nitrogen and oxygen to a gas mixture of $CH_4$ and $H_2$. The gas flow ratio of $CH_4$ to $H_2$ was 2.4:1, and 3% , 13.6% of nitrogen were added to the gas mixture of $CH_4$ and $H_2$ for the deposition of DLC films. The film stress tended to decrease as the nitrogen concentration increased from 3% to 13.6%, probably due to the decrease of the number of the interlink between carbon atoms. The residual stress tended to slightly decrease when 3% of oxygen was added. Scratch tests were performed to investigate the adhesion between the DLC films and the Ti intelayer after pretreating the TiN surface with direct hydrogen plasma. The adhesion was enhanced by adding nitrogen and oxygen to the $CH_4$ and $H_2$ gas mixture. The adhesion for the 3% nitrogen addition was better than that for the 13.6% nitrogen addition. The Vicker's hardness of the DLC films was measured to be 1100Hv.

• 한국추진공학회지
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• 제25권4호
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• pp.36-42
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• 2021

본 연구에서는 리오셀 섬유를 사용하여 연속식 흑연직물을 제조함에 있어, 리오셀 섬유에 phosphoric acid, ammonium phosphate, diammonium hydrogen, triammonium phosphate의 인계난연제를 처리 후 열중량, 푸리에변환적외선분광, C-핵자기공명분광, X-선 회절, 중량 분석을 통해 나타나는 물리적, 화학적 구조 변화에 대하여 고찰하였다. 인계난연제에 의한 열적 거동을 분석을 통해 내염화 공정의 온도, 가스, 처리시간 등에 대한 조건을 설정하였다. 연속식 내염화, 탄화, 흑연화 공정을 통해 인장강도 1,007.19±11.47 N/5 cm와 수율 25.3%의 흑연직물을 제조하였다.

• 한국수소및신에너지학회논문집
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• 제33권5호
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• pp.566-573
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• 2022

In this study, the mechanical properties of the polymer electrolyte membrane according to the temperature were studied. The test specimens of polymer electrolyte membrane were heat treated at 40℃, 60℃, 80℃, 100℃, and 120℃, and then the tensile tests were performed. As results of this study, the residual stress of the polymer electrolyte membrane was removes by the heat treatment and the elastic modulus decreased due to the decrease in internal energy. In addition, in the plastic region, the mechanical properties and crystallization rate of the polymer electrolyte membrane increased in proportion according to increase of the heat treatment temperature.

• Restorative Dentistry and Endodontics
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• 제26권5호
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• pp.399-408
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• 2001

Tooth bleaching has been prevailing recently for its ability to recover the color and shape of natural teeth without reduction of tooth material. However, it has been reported that bleaching procedure adversely affects the adhesive bond strength of composite resin to tooth. At the same time the bond strength was reported to be regained by application of some chemical agents. The purpose of this in vitro study was to investigate the effect of the removal of residual peroxide on the composite- enamel adhesion and also evaluated fracture mode between resin and enamel after bleaching. Sixty extracted human anterior and premolars teeth were divided into 5 groups and bleached by combined technique using of office bleaching with 35 % hydrogen peroxide and matrix bleaching with 10% carbamide peroxide for 4 weeks. After bleaching, the labial surfaces of each tooth were treated with catalase, 70% ethyl alcohol, distilled water and filled with composite resin. Shear bond strength was tested and the fractured surfaces were also examined with SEM. Analysis revealed significantly higher bond strength values. (p＜0.05) for catalase-treated specimens, but water-treated specimens showed reduction of bond strength, alcohol- treated specimens had medium value between the two groups(p＜0.05). The fracture mode was shown that the catalase group and the alcohol group had cohesive failure but the water sprayed group had adhesive failure. It was concluded that the peroxide residues in tooth after bleaching seems to be removed by gradual diffusion and the free radical oxygen from peroxide prevents polymerization by combining catalyst in the resin monomer. Therefore it may be possible to eliminate the adverse effect on the adhesion of composite resin to enamel after bleaching by using water displacement solution or dentin bonding agent including it for effective removal of residual peroxide.

• 대한기계학회논문집
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• 제11권2호
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• pp.314-321
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• 1987

본 논문에서는 용접열영향부(heat affected zone: HAZ)의 인성에 영향을 미치 는 인자중에서 잔유응력의 영향은 중대한 문제로 주목되고 있으며, 이로 인한 용접재 의 기계적 성질의 저하를 경함하기 위한 방법으로 용접후열처리(post weld heat trea- tment: PWHT)에 의한 제거방법을 이용하고 있다.그러나 이 열처리는 보톤 600.deg. C 이 상의 고온에서 실현되기 때문에 열처리과정에서 템퍼링(tempering)효과로 인한 HAZ의 열화가 때때로 발생하고 있어서 용접 시공상 문제로 되고 있다. 또한 PWHT시에는 가 열중이나 냉각중에도 열처리효과가 진행되고 있다고 볼 수 있으므로, PWHT가열속도는 기계적 성질의 개선이라는 이유외에 경제적 측면에서도 중요시 된다. 특히 용접조직 의 포화는 파괴의 양식에 직접반영되어, 파면형태의 차로 나타나므로, 본 조직의 포화 와 관련시켜 검토하기 위하여 열처리된 HAZ를 대상으로 작용된 응력의 크기와 가열속 도가 HAZ의 파괴인성에 어떠한 영향을 미치는지를 COD파괴인성시험과 미소경도측정, 그리고 주사전자현미경관찰을 통하여 고찰하였다.

• 펄프종이기술
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• 제46권3호
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• pp.20-27
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• 2014

Nowadays, the bleaching techniques of thermomechanical pulp(TMP) are fast developing on the strength of some benefits, mainly on low production cost and good fiber property. In this study, the optimum concentration of bleaching chemicals and the environmental load of bleaching wastes were considered to improve the bleaching efficiency of thermomechanical pulp using Korean redpine(Pinus densiflora) under the peroxide-based bleaching system. The optical property of TMP after bleaching was planned to use higher grade of paper, like printing & writting paper, not general newspaper. The concentration of bleaching chemicals, NaOH, $Na_2SiO_3$ and EDTA, in hydrogen peroxide bleaching system, on the basis of O.D. pulp was closely influenced on the improvement of TMP brightness. Final target of bleaching efficiency was set up to above 76%-ISO brightness. The optimal target brightness of Korean redpine TMP was reached to 76.45%-ISO under the conditions of $H_2O_2$ 7% with NaOH 2.20%, $Na_2SiO_3$ 0.63% and EDTA 0.02%. The concentration of NaOH, $Na_2SiO_3$ and EDTA was correlated functional to the residual peroxide content of wastewater, pH value and electric conductivity of TMP fibers after bleaching treatment. The optimal bleaching conditions by controlling the addition amount of chemicals were positively contributed to the brightness stabilization and environmental load of TMP.